The invention relates to a moisture activated barrier for an assembly. More particularly, the invention relates to a moisture activated barrier for composite insulators and surge arresters. The moisture activated barrier between the core and the housing of the assembly reacts with moisture that penetrates the housing to reseal the housing at the point of penetration.
Electrical transmission lines are typically supported by insulators mounted on poles. Insulators are used to prevent the loss of electric charge or current from conductors in electric power transmission lines. Composite insulators are typically composed of polymer weathersheds (which form a housing), a fiberglass reinforced plastic rod, and metal end fittings secured to each end of the rod. The polymer weathersheds may be bonded to the rod or a silicone compound may be applied at the housing-rod interface. The rod-end fitting combination is the mechanical load member for the insulator. The polymer housing protects the rod from the environment in addition to providing electrical leakage distance. Generally, the weathersheds and the rod are made from different materials especially suited for the distinct functions of the two components. In general, the rod takes the mechanical load.
Composite insulators are prone to failure when the rod comes into contact with moisture. Moisture invasion may happen for many reasons, such as deterioration of the housing due to prolonged exposure to the weather, poor insulator design, and gunfire vandalism. Furthermore, the site of moisture penetration remains open allowing more moisture to enter the housing since there is no means to seal the site of moisture penetration.
Examples of existing composite insulators are disclosed in the following references: U.S. Pat. No. 3,898,372 to Kalb; U.S. Pat. No. 4,656,555 to Raudabaugh; and U.S. Pat. No. 4,899,248 to Raudabaugh.
Surge arresters are commonly connected across a comparatively expensive piece of electrical equipment to shunt over-voltage surges. Such over-voltage surges occur, for example, when lightning strikes. When this happens, the surge arrester shunts the surge to ground, thereby protecting the piece of electrical equipment and the circuit from damage or destruction.
Surge arresters generally include an elongated, hollow cylindrical housing made of elastomeric material or the like, and a plurality of non-linear resistive blocks within the housing. The blocks commonly are metal oxide varistors (MOV), and are usually in the shape of relatively short cylinders stacked within the arrester housing. The number of blocks employed is a function of the material (MOV) and the voltage and current ratings of the assembly. For a surge arrester to function properly, the MOV blocks must be kept moisture free. Many existing surge arresters are susceptible to moisture invasion for many reasons, such as prolonged exposure to the weather, poor surge arrester design, and gunfire vandalism. Moreover, existing surge arresters have no means to prevent moisture that has entered the housing from contacting the MOV blocks. Furthermore, the site of moisture penetration remains open allowing more moisture to enter the housing since there is no means to seal the site of moisture penetration.
Examples of existing surge arresters are disclosed in the following references: U.S. Pat. No. 4,991,053 to Cunningham, U.S. Pat. No. 5,159,748 to Doone et al., and U.S. Pat. No. 5,043,838 to Sakich.
Thus, there is a continuing need to provide improved electrical assemblies having a moisture activated barrier to reseal any locations where moisture may penetrate the assembly, particularly for composite insulator and surge arrester assemblies.
Accordingly, it is a primary objective of the present invention to provide an assembly having a coating between the core and the housing that reseals the housing upon penetration by moisture, thereby extending the service life of the assembly.
Another object of the invention is to provide a composite insulator assembly having a moisture activated coating between the rod and the housing that reseals the housing upon penetration by moisture, thereby extending the service life of the composite insulator assembly.
A further objective of the present invention is to provide a surge arrester assembly having a moisture activated coating between the MOV blocks and the housing that reseals the housing upon penetration by moisture, thereby extending the service life of the surge arrester assembly.
The foregoing objects are attainable by providing an assembly provided having a core that has first and second ends and a housing. The housing has first and second ends and an internal passageway extending from the first housing end to the second housing end for receiving the core. A coating of an uncured moisture activated material is disposed between the housing and the core. The material cures upon reacting with moisture penetrating the housing to reseal the housing at a point of moisture penetration.
Other objects, advantages and salient features of the invention will become apparent from the following detailed description, which, taken in conjunction with the annexed drawings, discloses preferred embodiments of the invention.